The fourth lysine residue of histonine H3 (H3K4) appears to be the most extensively targeted histone methylation site, while mutations in 10 of its epigenetic regulators (KMT2A, KMT2C, KMT2D, KMT2F, KDM1A, KDM5A, KDM5B, KDM5C, PHF21A, and PHF8) have been associated with neurodevelopmental disorders (NDDs) [7]. The gene discussed is KDM5B; the disease is neurodevelopmental disorder.